As is well known, low pressure sodium lamps are among the most efficient light sources ever created by mankind. Efficiencies, especially at the high power levels, up to and exceeding 200 lumens per watt, have been demonstrated on commercial products. This has been the result of a lot of painstaking research and development and a lot of effort on the part of many people. Unfortunately, such a light source has a single atomic line with a yellow color, therefore it is a monochromatic radiation source. Objects under this light source look very awkward and appear as having unrealistic color. Therefore, this light source has not found a large acceptability in the marketplace. The primary application of such a light source has been in road illumination especially in Benelux countries and a few other countries around the world while the market penetration in the U.S. has been very little.
As mentioned above, for some roadway applications that might be acceptable because the color of objects is not really critical and in situations where energy savings is considered to be important such a light source has been utilized. Part of the reason for the increase in high efficiency of such a light source is the fact that the emission of sodium D lines, the principal component of the output of such a light source, falls very close to the maximum of the eye response and therefore a very small amount of radiation has a very high amount of visibility. This very same fact, however, has resulted in the light source not being acceptable for indoor general illumination applications such as offices, malls, and hotel applications.
It is an object of the present invention to provide a way of altering the color of a low pressure sodium light source so it appears white and therefore more acceptable in a variety of circumstances.
It is also an object of the present invention to provide a family of light sources of more acceptable color rendering index and high efficacy such that the field of applicability could be enhanced or widened to indoor as well as shop, factory, warehouse, motels, and high bay applications.
It is a further object of the present invention to provide an efficient white light source that has sufficient benefit to fit the applications of present day fluorescent lamps.
It is also an object of the present invention to provide a low pressure light source with a capability of compact configuration such that radiation in an acceptable white color is obtainable with high efficiency exceeding today's generally available efficiencies in compact fluorescent light sources.
Still further, it is an object of the present invention to enable a new family of light sources whereby a variety of power levels and applications could be demonstrated for general illumination.